DC-DC converting method and apparatus

ABSTRACT

A DC-DC converting apparatus including a step-up and step-down circuit stepping up/down an input voltage to generate an output voltage and a PWM control circuit. The PWM control circuit generates an error signal, first to third voltages, a first triangular wave signal varying between the first and second voltages, and a second triangular wave signal varying between the third voltage and a fourth voltage determined based on the first to third voltages. The PWM control circuit compares the error signal with the first and second triangular wave signals and causes the step-up and step-down circuit to step up/down the input voltage based on the comparison. The first to fourth voltages V1 to V4 satisfy V1&lt;V4&lt;V2&lt;V3 and V4=V3−(V2−V1). At least one of the first to third voltages is variably set to make a time in which voltage ranges of the first and second triangular wave signals overlap longer than a delay time caused by the comparison.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/153,544, filed on Jun. 16, 2005 now U.S. Pat. No. 7,202,644, theentire disclosure of which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

This patent application is based on and claims priority to Japanesepatent application No. 2004-178323 filed on Jun. 16, 2004 in the JapanPatent Office, the entire contents of which are incorporated byreference herein.

The invention relates to a DC-DC (direct current to direct current)converting method and apparatus, and more particularly to a DC-DCconverting method and apparatus which stably performs step-up andstep-down conversions by suitably setting a voltage range where avoltage range of a triangular wave signal used for a step-up controloverlaps a voltage range of a triangular wave signal used for astep-down control.

DISCUSSION OF THE BACKGROUND

In recent years, small-size mobile equipment, such as a mobile phone hasbeen widely used. Such small-size mobile equipment includes a small-sizerechargeable battery as a power source. To downsize batteries and extendtheir operation time, attempts have been made to improve batteryperformance and to reduce electric power consumption in small-sizemobile equipment. Further, it is desirable to widen a usable voltagerange of batteries to reduce the number of batteries and make themusable for a longer time. Therefore, some power supply circuits areprovided with a step-up and step-down DC-DC converter capable ofsupplying a load with a constant voltage even when a voltage provided bythe battery exceeds or falls below a voltage level required by the load.The step-up and step-down DC-DC converter is not selective in powersupply voltage and thus can adapt to a variety of power input such as abattery and an AC (alternating current) adapter.

FIG. 1 illustrates a configuration of a background step-up and step-downDC-DC converter 100. The step-up and step-down DC-DC converter 100includes an input terminal IN for receiving an input voltage VB, anoutput terminal OUT for outputting a predetermined output voltage Vout,a PWM (pulse-width modulation) control circuit 101, and a step-up and-down circuit 102.

The step-up and step-down circuit 102 includes an inductor La, acapacitor Ca, and transistors Ma to Md.

The PWM control circuit 101 includes an error amplifier circuit 111, atriangular wave generation circuit 112, a step-down comparator circuitCMPa, a step-up comparator circuit CMPb, a control circuit 113, and apredriver 114.

The error amplifier circuit 111 includes an operational amplifiercircuit AMPa, a reference voltage generation circuit 117, resistors R110and R111, and a feedback resistor R112. The reference voltage generationcircuit 117 generates and outputs a predetermined reference voltageVref. The resistors R110 and R111 divide the output voltage Vout andgenerate a feedback voltage VFB. The operational amplifier circuit AMPacompares the reference voltage Vref with the feedback voltage VFB, andgenerates and outputs an error signal Sa based on the result of thecomparison.

The triangular wave generation circuit 112 includes a first triangularwave generation circuit 121, a second triangular wave generation circuit122, a constant current source 123, a battery 124, and resistors R101 toR103. The first triangular wave generation circuit 121 generates a firsttriangular wave signal TWa used for performing a step-down control, andthe second triangular wave generation circuit 122 generates a secondtriangular wave signal TWb used for performing a step-up control.

The first triangular wave generation circuit 121 receives a firstvoltage Va used for setting a lower limit voltage of the firsttriangular wave signal TWa, a second voltage Vb used for setting anupper limit voltage of the first triangular wave signal TWa, and currentoutput from the constant current source 123 and used for setting agradient of a waveform of the first triangular wave signal TWa.

The second triangular wave generation circuit 122 receives a thirdvoltage Vc used for setting an upper limit voltage of the secondtriangular wave signal TWb, current output from the constant currentsource 123 and used for setting a gradient of the second triangular waveTWb, and a clock signal CLKa output from the first triangular wavegeneration circuit 121 to be used for synchronizing actions of thesecond triangular wave generation circuit 122. The currents input fromthe constant current source 23 to the first and second triangular wavegeneration circuits 121 and 122 are equal in value.

As illustrated in a timing diagram of FIG. 2, the first triangular wavesignal TWa forms a triangular waveform which varies between the firstvoltage Va and the second voltage Vb, while the second triangular wavesignal TWb forms a triangular waveform which varies between the thirdvoltage Vc and the fourth voltage Vd.

When the first triangular wave signal TWa reaches the first voltage Va(i.e., the lower limit voltage of the first triangular wave TWa), thefirst triangular wave generation circuit 121 outputs the clock signalCLKa to the second triangular wave generation circuit 122. Upon input ofthe clock signal CLKa to the second triangular wave generation circuit122, the voltage of the second triangular wave signal TWb which has beendecreasing starts to increase.

The gradients of the first and second triangular wave signals TWa andTWb are determined by the value of the current output from the constantcurrent source 123. Therefore, the first and second triangular wavesignals TWa and TWb have equal amplitudes. A fourth voltage Vd, which isa lower limit voltage of the second triangular wave signal TWb, is avoltage obtained by subtracting a voltage difference between the secondand first voltages Vb and Va from the third voltage Vc.

The fourth voltage Vd should be lower than the second voltage Vb tosmooth the switching between the step-up operation and the step-downoperation performed in the step-up and step-down DC-DC converter 100. Inother words, a voltage range of the first triangular wave signal TWaused for the step-down control should partly overlap a voltage range ofthe second triangular wave signal TWb used for the step-up control.

In a recent attempt to further reduce mobile equipment size and powerconsumption, a PWM control frequency of a step-up and step-down DC-DCconverter is increased. If the PWM control frequency is increased, theinductor La and the capacitor Ca which occupy space of the step-up andstep-down DC-DC converter may be downsized, and power efficiency may beimproved. The increase of the PWM control frequency is, therefore,effective in reducing electric power consumption.

If the PWM control frequency is increased, however, time periods Ta andTh shown in FIG. 2, in which the voltage range of the first triangularwave signal TWa overlaps the voltage range of the second triangular wavesignal TWb, are reduced.

As illustrated in FIG. 3, both the step-down comparator circuit CMPa andthe step-up comparator circuit CMPb have two types of delay timeperiods, i.e., first delay time periods TDa and TDb and second delaytime periods Tr and Tf. In the first delay time periods TDa and TDb, twoinput voltages input into the comparator circuit, reverse in voltagelevels, and affect the signal output from the comparator circuit. In thesecond delay time period Tr, which is a rise time of an output signaloutput from the comparator circuit, the output signal output from thecomparator circuit increases from a relatively low level (LOW) andreaches a relatively high level (HIGH). Meanwhile, in the second delaytime period Tf, which is a fall time of the output signal output fromthe comparator circuit, the output signal output from the comparatorcircuit decreases from the HIGH level and reaches the LOW level.

If each of the time periods Ta and Tb (i.e., the time periods in whichthe voltage range of the first triangular wave signal TWa overlaps thevoltage range of the second triangular wave signal TWb) is shorter thana sum of TDa, TDb, Tr, and Tf (i.e., TDa+TDb+Tr+Tf, which is hereinafterreferred to as a total delay time period), an effective output pulse isnot output during each of the time periods Ta and Tb from an outputterminal of the comparator circuit, and thus the step-up operation andthe step-down operation are prevented.

There is a background method of increasing currents consumed by thecomparator circuit to increase the operational speed and reduce thetotal delay time period of the comparator circuit. This method, however,contradicts the attempt to reduce electric power consumption byincreasing the PWM control frequency. That is, if the electric powerconsumption by the comparator circuit is increased, reduction inelectric power consumption may not be attained.

SUMMARY

The invention provides a DC-DC converting apparatus. In one example, aDC-DC converting apparatus includes a step-up and step-down circuit anda pulse-width modulation control circuit. The step-up and step-downcircuit is configured to step-up and step-down an input voltage togenerate and output a predetermined output voltage. The pulse-widthmodulation control circuit is configured to generate an error signalbased on the predetermined output voltage and a predetermined referencevoltage, first to third voltages, a first triangular wave signal varyingbetween the first and second voltages, and a second triangular wavesignal varying between the third voltage and a fourth voltage determinedbased on the first to third voltages. The pulse-width modulation controlcircuit is further configured to perform a comparison of the errorsignal with the first and second triangular wave signals, and to causethe step-up and step-down circuit to step-up and step-down the inputvoltage based on a result of the comparison. The first to fourthvoltages satisfy V1<V4<V2<V3 and V4=V3−(V2−V1), wherein V1 is the firstvoltage, V2 is the second voltage, V3 is the third voltage, and V4 isthe fourth voltage. Further, at least one of the first to third voltagesis variably set such that a time period in which the voltage ranges ofthe first and second triangular wave signals overlap, is longer than adelay time period caused by the comparison.

The invention further provides another DC-DC converting apparatus. Inone example, this DC-DC converting apparatus includes a step-up andstep-down circuit and a pulse-width modulation control circuit. Thestep-up and step-down circuit is configured to step-up and step-down aninput voltage according to a control signal input to generate and outputa predetermined output voltage. The pulse-width modulation controlcircuit is configured to generate an error signal indicating an error inthe feedback voltage proportional to the predetermined output voltageand a predetermined reference voltage, first to third voltages, a firsttriangular wave signal used for stepping down the input voltage, and asecond triangular wave signal used for stepping up the input voltage.The pulse-width modulation control circuit is further configured tocompare the error signal with the first and second triangular wavesignals, and to output the control signal to the step-up and step-downcircuit based on the result of the comparison. Further, the pulse-widthmodulation control circuit includes a triangular wave generation circuitand a comparator circuit. The triangular wave generation circuit isconfigured to set the first to third voltages and a fourth voltage so asto satisfy V1<V4<V2<V3 and V4=V3−(V2−V1), and to generate the first andsecond triangular wave signals, wherein V1 is the first voltage settinga lower limit voltage of the first triangular wave signal, V2 is thesecond voltage setting an upper limit voltage of the first triangularwave signal, V3 is the third voltage setting an upper limit voltage ofthe second triangular wave signal, and V4 is the fourth voltage settinga lower limit voltage of the second triangular wave signal. Thecomparator circuit is configured to compare the error signal with thefirst and second triangular wave signals. Further, at least one of thefirst to third voltages is variably set such that a time period in whichthe voltage ranges of the first and second triangular wave signalsoverlap is longer than a delay time period of the comparator circuit.

In the DC-DC converting apparatus, the triangular wave generationcircuit may include a constant voltage generation circuit, a constantcurrent source, a first triangular wave generation circuit, and a secondtriangular wave generation circuit. The constant voltage generationcircuit may be configured to generate and output the first to thirdvoltages. The constant current source may be configured to generate andoutput a predetermined constant current which is variably set to thedesired constant voltage and used for setting respective gradients ofthe first and second triangular wave signals. The first triangular wavegeneration circuit may be configured to receive the first and secondvoltages and the predetermined constant current and to generate andoutput the first triangular wave signal. The second triangular wavegeneration circuit may be configured to receive the third voltage andthe predetermined constant current and to generate and output the secondtriangular wave signal. In the DC-DC converting apparatus, at least oneof the first to third voltages may be variably set.

In the DC-DC converting apparatus, the constant voltage generationcircuit may include a first constant voltage source configured togenerate and output the second voltage which is variably set to thedesired constant voltage, a second constant voltage source configured togenerate and output the third voltage, and a voltage dividing circuitconfigured to divide the second voltage in order to generate and outputthe first voltage.

In the DC-DC converting apparatus, the constant voltage generationcircuit may include a first constant voltage source configured togenerate and output the second voltage which is variably set to thedesired constant voltage, a second constant voltage source configured togenerate and output the third voltage, and a voltage dividing circuitconfigured to divide the third voltage to generate and output the firstvoltage.

In the DC-DC converting apparatus, the constant voltage generationcircuit may include a first constant voltage source configured togenerate and output the second voltage which is variably set to thedesired constant voltage, a second constant voltage source configured togenerate and output the third voltage, and a third constant voltagesource configured to generate and output the first voltage.

In the DC-DC converting apparatus, the predetermined constant currentoutput from the constant current source may be variably set such thatfrequencies of the first and second triangular wave signals are keptconstant at predetermined values.

The invention further provides a DC-DC converting method for stepping upand stepping down an input voltage to generate and output apredetermined output voltage. In one example, a DC-DC converting methodfor stepping up and stepping down an input voltage to generate andoutput a predetermined output voltage includes: generating an errorsignal based on the predetermined output voltage and a predeterminedreference voltage; generating first to third voltages; generating afirst triangular wave signal varying between the first and secondvoltages and a second triangular wave signal varying between the thirdvoltage and a fourth voltage based on the first to third voltages;setting the first to fourth voltages so as to satisfy V1<V4<V2<V3 andV4=V3−(V2−V1), wherein V1 is the first voltage, V2 is the secondvoltage, V3 is the third voltage, and V4 is the fourth voltage;comparing the error signal with the first and second triangular wavesignals; and stepping up and stepping down the input voltage based on aresult of the comparison. In this method, at least one of the first tothird voltages V1 to V3 is variably set such that a time period in whichvoltage ranges of the first and second triangular wave signals overlapwith each other is longer than a delay time period caused by thecomparison.

The invention also provides another DC-DC converting method for steppingup and stepping down an input voltage to generate and output apredetermined output voltage. In one example, this DC-DC convertingmethod for stepping up and stepping down an input voltage to generateand output a predetermined output voltage includes: providing a step-upand step-down circuit and a pulse-width modulation control circuit;providing a triangular wave generation circuit and a comparator circuitin the pulse-width modulation control circuit; causing the pulse-widthmodulation control circuit to generate an error signal indicating anerror in the feedback voltage which is proportional to the predeterminedoutput voltage and a predetermined reference voltage; causing thetriangular wave generation circuit to set first to fourth voltages so asto satisfy V1<V4<V2<V3 and V4=V3−(V2−V1), and to generate a firsttriangular wave signal used for stepping down the input voltage and asecond triangular wave signal used for stepping up the input voltage,wherein V1 is the first voltage setting a lower limit voltage of thefirst triangular wave signal, V2 is the second voltage setting an upperlimit voltage of the first triangular wave signal, V3 is the thirdvoltage setting an upper limit voltage of the second triangular wavesignal, and V4 is the fourth voltage setting a lower limit voltage ofthe second triangular wave signal; causing the comparator circuit tocompare the error signal with the first and second triangular wavesignals; and causing the step-up and step-down circuit to step-up andstep-down the input voltage based on a result of the comparison. In thismethod, at least one of the first to third voltages is variably set suchthat a time period in which the voltage ranges of the first and secondtriangular wave signals overlap is longer than a delay time period ofthe comparator circuit.

The DC-DC converting method may further include, in the triangular wavegeneration circuit, a constant voltage generation circuit configured togenerate and output the first to third voltages, a constant currentsource configured to generate and output a predetermined constantcurrent which is variably set and used for setting the respectivegradients of the first and second triangular wave signals, a firsttriangular wave generation circuit configured to receive the first andsecond voltages and the predetermined constant current and to generateand output the first triangular wave signal, and a second triangularwave generation circuit configured to receive the third voltage and thepredetermined constant current and to generate and output the secondtriangular wave signal, and to variably set at least one of the first tothird voltages.

The DC-DC converting method may further include, in the constant voltagegeneration circuit, a first constant voltage source configured togenerate and output the second voltage which is variably set to thedesired constant voltage, a second constant voltage source configured togenerate and output the third voltage, and a voltage dividing circuitconfigured to divide the second voltage to generate and output the firstvoltage.

The DC-DC converting method may further include, in the constant voltagegeneration circuit, a first constant voltage source configured togenerate and output the second voltage which is variably set to thedesired constant voltage, a second constant voltage source configured togenerate and output the third voltage, and a voltage dividing circuitconfigured to divide the third voltage to generate and output the firstvoltage.

The DC-DC converting method may further include, in the constant voltagegeneration circuit, a first constant voltage source configured togenerate and output the second voltage which is variably set, a secondconstant voltage source configured to generate and output the thirdvoltage, and a third constant voltage source configured to generate andoutput the first voltage.

The DC-DC converting method may further include variably setting thepredetermined constant current output from the constant current sourcesuch that frequencies of the first and second triangular wave signalsare kept constant at predetermined values.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of theadvantages thereof are readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a circuit diagram illustrating a configuration of a backgroundstep-up and step-down DC-DC converter;

FIG. 2 is a timing diagram illustrating waveforms of first and secondtriangular wave signals generated in the step-up and step-down DC-DCconverter of FIG. 1;

FIG. 3 is a timing diagram illustrating delay time periods of astep-down comparator circuit and a step-up comparator circuit used inthe step-up and step-down DC-DC converter of FIG. 1;

FIG. 4 is a circuit diagram illustrating a configuration of a step-upand step-down DC-DC converter according to an exemplary embodiment ofthe invention;

FIG. 5 is a timing diagram illustrating relationships between first andsecond triangular wave signals and first to fourth voltages generated inthe step-up and step-down DC-DC converter of FIG. 4 according to anexemplary embodiment of the invention;

FIG. 6 provides timing diagrams illustrating changes of the first andsecond triangular wave signals generated in the step-up and step-downDC-DC converter of FIG. 4 according to an exemplary embodiment of theinvention;

FIG. 7 is a circuit diagram illustrating a configuration of a step-upand step-down DC-DC converter according to an exemplary embodiment ofthe invention;

FIG. 8 is a circuit diagram illustrating a configuration of a step-upand step-down DC-DC converter according to another exemplary embodimentof the invention;

FIG. 9 provides timing diagrams illustrating changes of the first andsecond triangular wave signals generated in the step-up and step-downDC-DC converter of FIG. 8 according to another exemplary embodiment ofthe invention; and

FIG. 10 is a circuit diagram illustrating a configuration of a step-upand step-down DC-DC converter according to an exemplary embodiment ofthe invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In describing preferred embodiments illustrated in the drawings,specific terminology is employed for the purpose of clarity. However,the disclosure of this patent specification is not intended to belimited to the specific terminology so used and it is to be understoodthat substitutions for each specific element can include any technicalequivalents that operate in a similar manner.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, moreparticularly to FIG. 4, which illustrates a configuration of a step-upand step-down DC-DC converter 200 according to an embodiment of theinvention.

The step-up and step-down DC-DC converter 200 of FIG. 4 includes aninput terminal IN, an output terminal OUT, a PWM control circuit 2, anda step-up and step-down circuit 3. The step-up and step-down DC-DCconverter 200 receives an input voltage VB input from the input terminalIN, converts the input voltage VB to a predetermined constant voltage,and outputs the predetermined constant voltage from the output terminalOUT as an output voltage Vout.

The PWM control circuit 2 includes a triangular wave generation circuit11, an error amplifier circuit 12, a step-down comparator circuit CMP1,a step-up comparator circuit CMP2, a control circuit 13, and a predriver14.

The triangular wave generation circuit 11 includes a first triangularwave generation circuit 21, a second triangular wave generation circuit22, a first constant voltage source 23, a second constant voltage source24, a constant current source 25, and resistors R1 and R2. The firsttriangular wave generation circuit 21 generates a first triangular wavesignal TW1 used for performing a step-down control, and the secondtriangular wave generation circuit 22 generates a second triangular wavesignal TW2 used for performing a step-up control. The first constantvoltage source 23 generates and outputs a second voltage V2 which isvariably set to the desired constant voltage. The second constantvoltage source 24 generates and outputs a predetermined third voltageV3. The constant current source 25 generates and outputs constantcurrent which is variably set to the desired constant voltage. Theresistors R1 and R2 divide the second voltage V2 to generate a firstvoltage V1. The step-down comparator circuit CMP1 and a step-upcomparator circuit CMP2 form a comparator circuit. The first constantvoltage source 23, the second constant voltage source 24, and theresistors R1 and R2 form a constant voltage generation circuit. Theresistors R1 and R2 form a voltage dividing circuit.

The resistors R1 and R2 are connected in series between the ground (GND)and the first constant voltage source 23 which outputs the secondvoltage V2. The first triangular wave generation circuit 21 receives thesecond voltage V2 used for setting an upper limit voltage of the firsttriangular wave signal TW1, and the first voltage V1 used for setting alower limit voltage of the first triangular wave signal TW1. The secondtriangular wave generation circuit 22 receives the third voltage V3 usedfor setting an upper limit voltage of the second triangular wave signalTW2, and a clock signal CLK1 output from the first triangular wavegeneration circuit 21 and used for synchronizing actions of the secondtriangular wave generation circuit 22. The first triangular wavegeneration circuit 21 and the second triangular wave generation circuit22 receive constant current output from the constant current source 25which are used for setting respective gradients of the first and secondtriangular wave signals TW1 and TW2. The first triangular wave signalTW1 output from the first triangular wave generation circuit 21 is inputin a non-inverting input terminal of the step-down comparator circuitCMP1, while the second triangular wave signal TW2 output from the secondtriangular wave generation circuit 22 is input in a non-inverting inputterminal of the step-up comparator circuit CMP2.

The error amplifier circuit 12 includes an operational amplifier circuitAMP1, a reference voltage generation circuit 31, resistors R10 and R11,and a feedback resistor R12. The reference voltage generation circuit 31generates and outputs a predetermined reference voltage Vref. Theresistors R10 and R11 divide the output voltage Vout and generate afeedback voltage VFB. The resistors R10 and R11 are connected in seriesbetween the output terminal OUT and the ground GND. An inverting inputterminal of the operational amplifier circuit AMP1 is connected to aconnection point between the resistors R10 and R11, while anon-inverting input terminal of the operational amplifier circuit AMP1receives input of the reference voltage Vref. The feedback resistor R12is connected between an output terminal of the operational amplifiercircuit AMP1 and the inverting input terminal of the operationalamplifier circuit AMP1. The output terminal of the operational amplifiercircuit AMP1 is connected to the inverting input terminal of thestep-down comparator circuit CMP1 and the inverting input terminal ofthe step-up comparator circuit CMP2. The operational amplifier circuitAMP1 compares the reference voltage Vref with the feedback voltage VFB,and generates and outputs an error signal S1 based on a result of thecomparison.

The step-down comparator circuit CMP1 compares a voltage of the firsttriangular wave signal TW1 with a voltage of the error signal S1 andoutputs a step-down mode switching signal S2, which is a binary signalindicating a result of the comparison, to the control circuit 13.

The step-up comparator circuit CMP2 compares a voltage of the secondtriangular wave signal TW2 with the voltage of the error signal S1 andoutputs a step-up mode switching signal S3, which is a binary signalindicating a result of the comparison, to the control circuit 13.

The control circuit 13 outputs a step-up and step-down control signal S4to the predriver 14 according to the step-down mode switching signal S2and the step-up mode switching signal S3 input therein.

The predriver 14 drives switching elements M1 to M4 of the step-up andstep-down circuit 3 according to the step-up and step-down controlsignal S4 input in the predriver 14 from the control circuit 13.

The step-up and step-down circuit 3 includes the switching elements M1to M4, an inductor L1, and a capacitor C1. The switching elements M1 andM2 are NMOS (N-channel metal oxide semiconductor) transistors whichperform a step-down control to the output voltage Vout. Meanwhile, theswitching elements M3 and M4 are NMOS transistors which perform astep-up control to the output voltage Vout. The step-up and step-downcircuit 3 performs a step-up operation and a step-down operation of theoutput voltage Vout according to switching signals S11 to S14 outputfrom the predriver 14 of the PWM control circuit 2.

The switching element M1 and M2 are connected in series between theinput terminal IN and the ground GND, while the switching elements M3and M4 are connected in series between the output terminal OUT and theground GND. The inductor L1 is connected between a connection point ofthe switching elements M1 and M2 and a connection point of the switchingelements M3 and M4. The capacitor C1 is connected between the outputterminal OUT and the ground GND. The switching signals S11 to S14 outputfrom the predriver 14 are input in corresponding gates of the switchingelements M1 to M4.

Operations of the step-up and step-down DC-DC converter 200 shown inFIG. 4 is described with reference to FIG. 5, which is a timing diagramillustrating the relationships between the first triangular wave signalTW1, the second triangular wave signal TW2, and the first to fourthvoltages V1 to V4.

As illustrated in FIG. 5, the first triangular wave signal TW1 forms awaveform which varies between the first voltage V1 and the secondvoltage V2, while the second triangular wave signal TW2 forms a waveformwhich varies between the third voltage V3 and the fourth voltage V4.

The fourth voltage V4 shown in FIG. 5 is a lower limit voltage of thesecond triangular wave TW2. When the first triangular wave signal TW1reaches the first voltage V1 (i.e., the lower limit voltage of the firsttriangular wave signal TW1), the first triangular wave generationcircuit 21 outputs the clock signal CLK1 to the second triangular wavegeneration circuit 22. Upon input of the clock signal CLK1 to the secondtriangular wave generation circuit 22, the voltage of the secondtriangular wave signal TW2, which has been decreasing, starts toincrease.

The gradients of the first and second triangular wave signals TW1 andTW2 are determined by a value of the constant current output from theconstant current source 25. Therefore, the first and second triangularwave signals TW1 and TW2 have equal amplitudes. The fourth voltage V4(i.e., the lower limit voltage of the second triangular wave signal TW2)is a voltage obtained by subtracting a voltage difference between thesecond and first voltages V2 and V1 from the third voltage V3. That is,the fourth voltage V4 is expressed as V4=V3−(V2−V1). The fourth voltageV4 should be lower than the second voltage V2 to smooth the switchingbetween the step-up operation and the step-down operation performed inthe step-up and step-down DC-DC converter 200. In other words, a voltagerange of the first triangular wave signal TW1 used for the step-downcontrol should partly overlap a voltage range of the second triangularwave signal TW2 used for the step-up control.

When the input voltage VB is lower than the output voltage Vout, avoltage of the error signal S1 output from the operational amplifierAMP1 falls between the second voltage V2 and the third voltage V3.Accordingly, the step-up comparator circuit CMP2 outputs the step-upmode switching signal S3 to the control circuit 13, and the step-upoperation is performed to control the output voltage Vout to apredetermined level. When the output voltage Vout decreases, the voltageof the error signal S1 increases, and the step-up operation is performedto control the output voltage Vout to increase up to a predeterminedlevel.

When the input voltage VB is higher than the output voltage Vout, on theother hand, the voltage of the error signal S1 falls between the firstvoltage V1 and the fourth voltage V4. Accordingly, the step-downcomparator circuit CMP1 outputs the step-down mode switching signal S2to the control circuit 13, and the step-down operation is performed tocontrol the output voltage Vout to a predetermined level. When theoutput voltage Vout decreases, the voltage of the error signal S1decreases, and the step-down operation is performed to control theoutput voltage Vout to increase up to a predetermined level.

When the input voltage VB and the output voltage Vout are at anapproximately equal level, the voltage of the error signal S1 fallsbetween the fourth voltage V4 and the second voltage V2. Accordingly,the step-down comparator circuit CMP1 outputs the step-down modeswitching signal S2 to the control circuit 13, and the step-upcomparator circuit CMP2 outputs the step-up mode switching signal S3 tothe control circuit 13. As a result, the step-up operation and thestep-down operation are performed, respectively, to control the outputvoltage Vout to be at a predetermined level.

FIGS. 6( a) and 6(b) illustrate changes of the first triangular wavesignal TW1 and the second triangular wave signal TW2 generated in thestep-up and step-down DC-DC converter 200 of FIG. 4. FIG. 6( a)illustrates an example of an initial state in which the second voltageV2 (i.e., the output voltage output from the first constant voltagesource 23) is set at 0.8 volts, and the first voltage V1 is set at 0.2volts, for example. Further, the third voltage V3 (i.e., the outputvoltage output from the second constant voltage source 24) is set at 1.2volts, for example. In this case, the fourth voltage V4 becomes 0.6volts according to the above equation V4=V3−(V2−V1), and a voltage rangein which the voltage range of the first triangular wave signal TW1overlaps the voltage range of the second triangular wave signal TW2 is0.2 volts (i.e., 0.8−0.6=0.2).

FIG. 6( b) illustrates a state in which the second voltage V2 isincreased from 0.8 volts to 0.85 volts. In this case, the first voltageV1 increases to 0.21 volts, and the third voltage V3 stays unchanged at1.2 volts. The fourth voltage V4 becomes 0.56 volts according to theabove equation V4=V3−(V2−V1). Accordingly, the voltage range in whichthe voltage range of the first triangular wave signal TW1 overlaps thevoltage range of the second triangular wave signal TW2 is 0.29 volts(i.e., 0.85−0.56=0.29), which is 0.09 volts larger than 0.2 volts of theinitial state.

As observed from FIGS. 6( a) and 6(b), time periods T1 and T2, in whichthe voltage range of the first triangular wave signal TW1 overlaps withthe voltage range of the second triangular wave signal TW2 arerespectively longer in FIG. 6( b) than in FIG. 6( a). If an outputvoltage output from the first constant voltage source 23 is increased,the PWM control frequency slightly decreases but can be restored byadjusting the value of the constant current output from the constantcurrent source 25.

FIG. 7 illustrates a configuration of a step-up and step-down DC-DCconverter 300 according to another exemplary embodiment of theinvention. A detailed description is omitted for the components shown inFIG. 7, which were described with reference to FIG. 4. However, thedifferences between the step-up and step-down DC-DC converter 200 ofFIG. 4 and the step-up and step-down DC-DC converter 300 of FIG. 7 aredescribed. The step-up and step-down DC-DC converter 300 is differentfrom the step-up and step-down DC-DC converter 200 in that the resistorsR1 and R2 are replaced by a third constant voltage source 27 in thestep-up and step-down DC-DC converter 300. In this case, the thirdconstant voltage source 27 generates and outputs the first voltage V1which is variably set to the desired voltage. The first constant voltagesource 23, the second constant voltage source 24, and the third constantvoltage source 27 form a constant voltage generation circuit. With thisconfiguration, the step-up and step-down DC-DC converter 300 can providesimilar operation of the step-up and step-down DC-DC converter 200.

As described above, in the step-up and step-down DC-DC converters 200and 300, the value of the second voltage V2 output from the firstconstant voltage source 23 is set such that the time periods T1 and T2,in which the voltage range of the first triangular wave signal TW1overlaps the voltage range of the second triangular wave signal TW2, arelonger than the delay time periods of the step-down comparator circuitCMP1 and the step-up comparator circuit CMP2. Accordingly, the step-upoperation and the step-down operation of the output voltage Vout can beperformed even during the time periods T1 and T2 in which the voltagerange of the first triangular wave signal TW1 overlaps the voltage rangeof the second triangular wave signal TW2. As a result, the outputvoltage Vout can be stabilized.

A constant voltage source outputting a constant voltage which isvariably set to the desired constant voltage may be used as the secondconstant voltage source 24 in the step-up and step-down DC-DC converters200 and 300. With this configuration, the third voltage V3 may bedecreased to extend the time periods T1 and T2, in which the voltagerange of the first triangular wave signal TW1 overlaps the voltage rangeof the second triangular wave signal TW2. In this case, however, thehighest voltage within a voltage range of the error signal S1 isdecreased, and thus this method of decreasing the third voltage V3 toincrease the time periods T1 and T2 is limited to when the error signalS1 has a relatively sufficient voltage range.

The first voltage V1 is generated by dividing the second voltage V2 inthe step-up and step-down DC-DC converters 200. Alternatively, the firstvoltage V1 may be generated by dividing the third voltage V3, as in astep-up and step-down DC-DC converters 400 according to anotherembodiment.

FIG. 8 illustrates a configuration of the step-up and step-down DC-DCconverters 400. A detailed description is omitted for the componentsshown in FIG. 8, which were described with reference to FIG. 4. However,the differences between the step-up and step-down DC-DC converters 200of FIG. 4 and the step-up and step-down DC-DC converter 400 of FIG. 8are described. The step-up and step-down DC-DC converter 400 isdifferent from the step-up and step-down DC-DC converters 200 in thatthe resistors R1 and R2 of the step-up and step-down DC-DC converter 200are replaced by resistors R3 and R4 which divide the third voltage V3 togenerate the first voltage V1.

The step-up and step-down DC-DC converter 400 includes the inputterminal IN, the output terminal OUT, a PWM control circuit 2 a, and thestep-up and the step-down circuit 3.

The PWM control circuit 2 a includes a triangular wave generationcircuit 11 a, the error amplifier circuit 12, the step-down comparatorcircuit CMP1, the step-up comparator circuit CMP2, the control circuit13, and the predriver 14.

The triangular wave generation circuit 11 a includes the firsttriangular wave generation circuit 21, the second triangular wavegeneration circuit 22, the first constant voltage source 23, the secondconstant voltage source 24, the constant current source 25, and theresistors R3 and R4. The first constant voltage source 23, the secondconstant voltage source 24, and the resistors R3 and R4 form a constantvoltage generation circuit. The resistors R3 and R4 form a voltagedividing circuit.

The resistors R3 and R4 are connected in series between the ground GNDand the second constant voltage source 24 which outputs the thirdvoltage V3. The first triangular wave generation circuit 21 receives thesecond voltage V2 used for setting the upper limit voltage of the firsttriangular wave signal TW1, and the first voltage V1 which is generatedby dividing the third voltage V3 with the resistors R3 and R3 and whichis used for setting the lower limit voltage of the first triangular wavesignal TW1.

FIGS. 9( a) and 9(b) illustrate changes of the first triangular wavesignal TW1 and the second triangular wave signal TW2 generated in thestep-up and step-down DC-DC converter 400 of FIG. 8. FIG. 9( a)illustrates an example of an initial state in which the third voltage V3(i.e., the output voltage output from the second constant voltage source24) is set at 1.2 volts, and the first voltage V1 is set at 0.2 volts,for example. Further, the second voltage V2 (i.e., the output voltageoutput from the first constant voltage source 23) is set at 0.8 volts,for example. In this case, the fourth voltage V4 becomes 0.6 voltsaccording to the equation V4=V3−(V2−V1), and a voltage range in whichthe voltage range of the first triangular wave signal TW1 overlaps thevoltage range of the second triangular wave signal TW2 is 0.2 volts(i.e., 0.8−0.6=0.2).

FIG. 9( b) illustrates a state in which the second voltage V2 isincreased from 0.8 volts to 0.85 volts. In this case, the first voltageV1 and the third voltage V3 stay unchanged at 0.2 volts and 1.2 volts,respectively. The fourth voltage V4 becomes 0.55 volts according to theabove equation V4=V3−(V2−V1). Accordingly, the voltage range in whichthe voltage range of the first triangular wave signal TW1 overlaps thevoltage range of the second triangular wave signal TW2 is 0.3 volts(i.e., 0.85−0.55=0.3), which is 0.1 volts larger than the 0.2 volts ofthe initial state.

As observed from FIGS. 9( a) and 9(b), the time periods T1 and T2, inwhich the voltage range of the first triangular wave signal TW1 overlapsthe voltage range of the second triangular wave signal TW2 arerespectively longer in FIG. 9( b) than in FIG. 9( a). If the outputvoltage output from the first constant voltage source 23 is increased,the PWM control frequency decreases, as in the case of the step-up andstep-down DC-DC converter 200 shown in FIG. 4. Therefore, variation inthe PWM control frequency is cancelled out by increasing the value ofthe constant current output from the constant current source 25.

FIG. 10 illustrates a configuration of a step-up and step-down DC-DCconverter 500 according to another embodiment of the invention. Adetailed description is omitted for the components shown in FIG. 10which were described with reference to FIGS. 4 and 8. However, thedifferences between the step-up and step-down DC-DC converter 400 ofFIG. 8 and the step-up and step-down DC-DC converter 500 of FIG. 10 aredescribed. The step-up and step-down DC-DC converter 500 is differentfrom the a step-up and step-down DC-DC converter 400 in that theresistors R3 and R4 are replaced by a third constant voltage source 28in the step-up and step-down DC-DC converter 500. The third constantvoltage source 28 generates and outputs the first voltage V1. The firstconstant voltage source 23, the second constant voltage source 24, andthe third constant voltage source 28 form a constant voltage generationcircuit. With this configuration, the step-up and step-down DC-DCconverter 500 can provide similar operations of the step-up andstep-down DC-DC converter 400.

As described above, in the step-up and step-down DC-DC converter 400,the first voltage V1 is generated by dividing the third voltage V3.Accordingly, the step-up and step-down DC-DC converter 400 can provide asimilar effect to that of the step-up and step-down DC-DC converter 200.

Further, a constant voltage source outputting a constant voltage whichis variably set to the desired constant voltage may be used as thesecond constant voltage source 24 in the step-up and step-down DC-DCconverters 400 and 500. With this configuration, the third voltage V3may be decreased to increase the time periods T1 and T2, in which thevoltage range of the first triangular wave signal TW1 overlaps thevoltage range of the second triangular wave signal TW2. In this case,however, the highest voltage within a voltage range of the error signalS1 is decreased, and thus this method of decreasing the third voltage V3to increase the time periods T1 and T2 is limited to when the errorsignal S1 has a relatively sufficient voltage range.

Two constant voltage sources are used in each of the step-up andstep-down DC-DC converters 200 and 400. Alternatively, the third voltageV3 may be generated from the first voltage V1 by using a constantvoltage source outputting a constant voltage which is variably set tothe desired constant voltage and at least three resistors that dividethe output voltage output from the constant voltage source. Further, thestep-up and step-down DC-DC converter may be provided with a constantvoltage source which generates the first voltage V1, constant voltagesources which respectively generate the second voltage V2 and the thirdvoltage V3 which are variably set to the desired constant voltage, andseries-connected resistors. If more than one constant voltage sourcesare provided in the step-up and step-down DC-DC converter, the first tothird voltages V1 to V3 change in values, depending on which constantvoltage source is configured to output a constant voltage which isvariably set to the desired constant voltage. Circuits used in thestep-up and step-down DC-DC converter should be appropriately chosenaccording to purposes.

The above-described embodiments are illustrative, and numerousadditional modifications and variations are possible in light of theabove teachings. For example, elements and/or features of differentillustrative and exemplary embodiments herein may be combined with eachother and/or substituted for each other within the scope of thisdisclosure and appended claims. It is therefore to be understood thatwithin the scope of the appended claims, the disclosure of this patentspecification may be practiced otherwise than as specifically describedherein.

1. A DC-DC converting apparatus comprising: a step-up and step-downcircuit configured to step-up and step-down an input voltage to generateand output a predetermined output voltage; and a pulse-width modulationcontrol circuit configured to: generate an error signal based on thepredetermined output voltage and a predetermined reference voltage,first to third voltages, a first triangular wave signal varying betweenthe first and second voltages, and a second triangular wave signalvarying between the third voltage and a fourth voltage, determined basedon the first to third voltages, perform a comparison of the error signalwith the first and second triangular wave signals, and cause the step-upand step-down circuit to step-up and step-down the input voltage basedon a result of the comparison, wherein at least one of the first tothird voltages is variably set such that a time period in which voltageranges of the first and second triangular wave signals overlap is longerthan a delay time period caused by the comparison.
 2. A DC-DC convertingapparatus comprising: a step-up and step-down circuit configured tostep-up and step-down an input voltage according to a control signalinput therein to generate and output a predetermined output voltage; anda pulse-width modulation control circuit configured to: generate anerror signal indicating an error in a feedback voltage proportional tothe predetermined output voltage and a predetermined reference voltage,first to third voltages, a first triangular wave signal configured forstepping down the input voltage, and a second triangular wave signalconfigured for stepping up the input voltage, compare the error signalwith the first and second triangular wave signals, and output thecontrol signal to the step-up and step-down circuit based on a result ofthe comparison, wherein at least one of the first to third voltages isvariably set such that a time period in which voltage ranges of thefirst and second triangular wave signals overlap is longer than a delaytime period of the comparator circuit.
 3. The DC-DC converting apparatusas described in claim 2, wherein the triangular wave generation circuitcomprises: a constant voltage generation circuit configured to generateand output the first to third voltages; a constant current sourceconfigured to generate and output predetermined constant current whichis variably set and used for setting respective gradients of the firstand second triangular wave signals; a first triangular wave generationcircuit configured to receive the first and second voltages and thepredetermined constant current and to generate and output the firsttriangular wave signal; and a second triangular wave generation circuitconfigured to receive the third voltage and the predetermined constantcurrent and to generate and output the second triangular wave signal,wherein at least one of the first to third voltages is variably set. 4.The DC-DC converting apparatus as described in claim 3, wherein theconstant voltage generation circuit comprises: a first constant voltagesource configured to generate and output the second voltage which isvariably set; a second constant voltage source configured to generateand output the third voltage; and a voltage dividing circuit configuredto divide the second voltage to generate and output the first voltage.5. The DC-DC converting apparatus as described in claim 3, wherein theconstant voltage generation circuit comprises: a first constant voltagesource configured to generate and output the second voltage which isvariably set; a second constant voltage source configured to generateand output the third voltage; and a voltage dividing circuit configuredto divide the third voltage to generate and output the first voltage. 6.The DC-DC converting apparatus as described in claim 3, wherein theconstant voltage generation circuit comprises: a first constant voltagesource configured to generate and output the second voltage which isvariably set; a second constant voltage source configured to generateand output the third voltage; and a third constant voltage sourceconfigured to generate and output the first voltage.
 7. The DC-DCconverting apparatus as described in claim 3, wherein the predeterminedconstant current output from the constant current source is variably setsuch that frequencies of the first and second triangular wave signalsare kept constant at predetermined values.
 8. A DC-DC convertingapparatus comprising: step-up and step-down means for stepping up andstepping down an input voltage to generate and output a predeterminedoutput voltage; and pulse-width modulation control means for: generatingan error signal based on the predetermined output voltage and apredetermined reference voltage, first to third voltages, a firsttriangular wave signal varying between the first and second voltages,and a second triangular wave signal varying between the third voltageand a fourth voltage determined based on the first to third voltages,performing a comparison of the error signal with the first and secondtriangular wave signals, and causing the step-up and step-down circuitto step-up and step-down the input voltage based on a result of thecomparison, wherein at least one of the first to third voltages isvariably set such that a time period in which voltage ranges of thefirst and second triangular wave signals overlap is longer than a delaytime period caused by the comparison.
 9. A DC-DC converting apparatuscomprising: step-up and step-down means for stepping up and steppingdown an input voltage according to a control signal input therein togenerate and output a predetermined output voltage; and pulse-widthmodulation control means for: generating an error signal indicating anerror in a feedback voltage proportional to the predetermined outputvoltage and a predetermined reference voltage, first to third voltages,a first triangular wave signal used for stepping down the input voltage,and a second triangular wave signal used for stepping up the inputvoltage, comparing the error signal with the first and second triangularwave signals, and outputting the control signal to the step-up andstep-down circuit based on a result of the comparison, wherein at Leastone of the first to third voltages is variably set such that a timeperiod in which voltage ranges of the first and second triangular wavesignals overlap is longer than a delay time period of the comparatormeans.
 10. The DC-DC converting apparatus as described in claim 9,wherein the triangular wave generation means comprises: constant voltagegeneration means for generating and outputting the first to thirdvoltages; constant current source means for generating and outputtingpredetermined constant current which is variably set and used forsetting respective gradients of the first and second triangular wavesignals; first triangular wave generation means for receiving the firstand second voltages and the predetermined constant current, and forgenerating and outputting the first triangular wave signal; and secondtriangular wave generation means for receiving the third voltage and thepredetermined constant current, and for generating and outputting thesecond triangular wave signal, wherein at least one of the first tothird voltages is variably set.
 11. The DC-DC converting apparatus asdescribed in claim 10, wherein the constant voltage generation meanscomprises: first constant voltage source means for generating andoutputting the second voltage which is variably set; second constantvoltage source means for generating and outputting the third voltage;and voltage dividing means for dividing the second voltage to generateand output the first voltage.
 12. The DC-DC converting apparatus asdescribed in claim 10, wherein the constant voltage generation meanscomprises: first constant voltage source means for generating andoutputting the second voltage which is variably set second constantvoltage source means for generating and outputting the third voltage;and voltage dividing means for dividing the third voltage to generateand output the first voltage.
 13. The DC-DC converting apparatus asdescribed in claim 10, wherein the constant voltage generation meanscomprises: first constant voltage source means for generating andoutputting the second voltage which is variably set; second constantvoltage source means for generating and outputting the third voltage;and third constant voltage source means for generating and outputtingthe first voltage.
 14. The DC-DC converting apparatus as described inclaim 10, wherein the predetermined constant current output from theconstant current source means is variably set such that frequencies ofthe first and second triangular wave signals are kept constant atpredetermined values.
 15. A DC-DC converting method for stepping up andstepping down an input voltage to generate and output a predeterminedoutput voltage, the DC-DC converting method comprising the steps of:generating an error signal based on the predetermined output voltage anda predetermined reference voltage; generating first to third voltages;generating a first triangular wave signal varying between the first andsecond voltages and a second triangular wave signal varying between thethird voltage and a fourth voltage determined based on the first tothird voltages; comparing the error signal with the first arid secondtriangular wave signals; and stepping up and stepping down the inputvoltage based on a result of the comparison, wherein at least one of thefirst to third voltages is variably set such that a time period in whichvoltage ranges of the first and second triangular wave signals overlapis longer than a delay time period caused by the comparison.
 16. A DC-DCconverting method for stepping up and stepping down an input voltage togenerate and output a predetermined output voltage, the DC-DC convertingmethod comprising the steps of: providing a step-up and step-downcircuit and a pulse-width modulation control circuit; providing atriangular wave generation circuit and a comparator circuit in thepulse-width modulation control circuit; causing the pulse-widthmodulation control circuit to generate an error signal indicating anerror in a feedback voltage proportional to the predetermined outputvoltage and a predetermined reference voltage; generating a firsttriangular wave signal used for stepping down the input voltage and asecond triangular wave signal used for stepping up the input voltage,causing the comparator circuit to compare the error signal with thefirst and second triangular wave signals; and causing the step-up andstep-down circuit to step-up and step-down the input voltage based on aresult of the comparison, wherein at least one of the first to thirdvoltages is variably set such that a time period in which voltage rangesof the first and second triangular wave signals overlap is longer than adelay time period of the comparator circuit.
 17. The DC-DC convertingmethod as described in claim 16, further comprising the step of:including, in the triangular wave generation circuit: a constant voltagegeneration circuit configured to generate and output the first to thirdvoltages, a constant current source configured to generate and outputpredetermined constant current which is variably set and used forsetting respective gradients of the first and second triangular wavesignals, a first triangular wave generation circuit configured toreceive the first and second voltages and the predetermined constantcurrent and to generate and output the first triangular wave signal, anda second triangular wave generation circuit configured to receive thethird voltage and the predetermined constant current and to generate andoutput the second triangular wave signal; and variably setting at leastone of the first to third voltages.
 18. The DC-DC converting method asdescribed in claim 17, further comprising the step of: including, in theconstant voltage generation circuit: a first constant voltage sourceconfigured to generate and output the second voltage which is variablyset, a second constant voltage source configured to generate and outputthe third voltage, and a voltage dividing circuit configured to dividethe second voltage to generate and output the first voltage.
 19. TheDC-DC converting method as described in claim 17, further comprising thestep of: including, in the constant voltage generation circuit: a firstconstant voltage source configured to generate and output the secondvoltage which is variably set, a second constant voltage sourceconfigured to generate and output the third voltage, and a voltagedividing circuit configured to divide the third voltage to generate andoutput the first voltage.
 20. The DC-DC converting method as describedin claim 17, further comprising the step of: including, in the constantvoltage generation circuit: a first constant voltage source configuredto generate and output the second voltage which is variably set, asecond constant voltage source configured to generate and output thethird voltage, and a third constant voltage source configured togenerate and output the first voltage.
 21. The DC-DC converting methodas described in claim 17, further comprising the step of: variablysetting the predetermined constant current output from the constantcurrent source such that frequencies of the first and second triangularwave signals are kept constant at predetermined values.
 22. A DC-DCconverting apparatus comprising: a step-up and step-down circuitconfigured to step-up and step-down an input voltage to generate andoutput a predetermined output voltage; and a pulse-width modulationcontrol circuit configured to: generate an error signal based on thepredetermined output voltage and a predetermined reference voltage andthe first to third voltages, a first triangular wave signal, and asecond triangular wave signal, perform a comparison of the error signalwith the first and second triangular wave signals, and cause the step-upand step-down circuit to step-up and step-down the input voltage basedon a result of the comparison, wherein at least one of the first tothird voltages is variably set such that a time period in which voltageranges of the first and second triangular wave signals overlap is longerthan a delay time period caused by the comparison.